Characterization of a Low Molecular Weight Na‐K-ATPase Inhibitor of Urinary Origin
作者:
ELMAR WEILER,
HARVEY GONICK,
BRUCE PRINS,
RALPH PURDY,
M. WEBER,
期刊:
The American Journal of the Medical Sciences
(OVID Available online 1994)
卷期:
Volume 307,
issue 1
页码: 27-35
ISSN:0002-9629
年代: 1994
出版商: OVID
关键词: Na-K-ATPase;K-pNPPase;Sodium-potassium-activated adenosine-triphosphatase inhibitor;3H-ouabain displacement;Digoxin-like immunoreactivity;Enzyme kinetics
数据来源: OVID
摘要:
It has been demonstrated that expansion of extracellular fluid volume induces the release of a low-molecular-weight natriuretic and sodium-potassium-activated adenosine triphosphatase inhibiting hormone (NKAI). In this study, we used a highly purified hormone extracted from pooled hypertensive urines (u-NKAI). Like ouabain, this compound was found to be a potent inhibitor of the sodium-potassium-activated adenosine-triphosphatase and potassium-stimulated paranitrophenyl phosphatase enzyme systems as well as a vasoconstrictor in vitro. In contrast to ouabain, which is a competitive inhibitor of both enzyme systems with respect to potassium, u-NKAI is noncompetitive. Furthermore, u-NKAI differs from ouabain by its lack of cross-reactivity with digoxin antibodies. In addition, whereas ouabain binds to both high-affinity and low-affinity binding sites on the sodium-potassium-activated adenosine-triphosphatase enzyme in the absence of potassium, u-NKAI binds only to the low-affinity binding sites. This study demonstrates that the highly purified u-NKAI, although ouabain-like in certain respects, is not an “endogenous ouabain.”
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